1. Field of the Invention:
The present invention relates to a debarking apparatus. More particularly, the invention relates to an apparatus for removing the bark from tree-length logs by causing the logs to rub against one another.
2. Discussion of Background:
Many industrial processes use cut logs from which the bark has been removed. For example, trees are felled, cut into appropriate lengths, stripped of bark before being cut into lumber, manufactured into such products as waferboard and particleboard, or processed into chips for paper-making. The stripped bark may be recovered and used as mulch.
Many types of apparatus are available for debarking logs. Hydraulic peelers direct a stream of pressurized water onto the logs to strip off the bark. Ramsdell, et al. (U.S. Pat. No. 2,829,687) use toothed wheels mounted at an oblique angle with respect to the axis of the log to both turn and advance a log while cutter wheels peel off the bark. More commonly, logs are tumbled in contact with one another in a drum debarker. Bark is rubbed from the exposed surfaces of the logs through contact with the other logs. Drum debarkers consist of a series of large cylinders rotating about their longitudinal axes. Logs are fed upwardly along the rising side of the cylinder. The rotating of the cylinder causes them to roll back towards the opposite side.
Other debarking devices have stationary housings having endless conveyors that move the lowermost logs toward the top, then release the logs to create the tumbling action that debarks the logs. See, e.g., Hillbom (U.S. Pat. No. 2,137,451; Sweden No. 117,703), Ullgren (U.S. Pat. No. 2,125,529), Thorne (U.S. 1,319,935), Olsson (Sweden 94,176), Johansson, et al. (Sweden 88,737). Logs may be moved back and forth both lengthwise and sideways to induce rubbing and shearing action between their exposed surfaces (Wallin, U.S. Pat. No. 4,805,677), or advanced laterally while being tumbled, as in the linked drum sections of Carbonneau (U.S. Pat. No. 3,973,606). Ferrabee (U.S. Pat. No. 3,228,440; Canada 734,238) uses a plurality of movable staves tilted at a desired angle to lift and tumble logs entering the apparatus. The greater the angle, the sooner the logs exit the device. Nilsson, et al. (Sweden 154,817) use chain-driven teeth of different shapes to tilt logs at a desired angle for moving the logs forward. Chain drives are also used in devices for trimming branches from cut trees, as described by Glebov, et al. (U.S.S.R. 309,818).
The ease of debarking is related to the type of wood and the temperature of the logs. Conifers, for example, are easier to debark than deciduous trees such as aspen or oak. In general, debarking is easier in summer than in winter, and easier in warm climates than in cold climates. In winter, especially at northern latitudes where freezing is common, logs may be soaked in water or sprayed with water or steam to facilitate loosening of the bark and speed the debarking process. See, e.g., Hillbom (U.S. Pat. No. 2,137,451), Ormell (Sweden 95,161; 87,449), Olsson (Sweden No. 94,176).
Debarkers are generally designed for batch-processing logs cut to standard lengths such as four feet (about 1.2 m) and eight feet (about 2.4 m) rather than whole logs. Drum debarkers can process whole logs but not without some difficulty. Many debarkers require a crane to hoist a load of logs from a truck or stockpile to their feed end so that the logs move by gravity forward to the exit end.
There is a need for a debarking apparatus that effectively removes bark from full-length cut trees, that processes the logs continuously rather than batchwise and that is easy to feed logs into.